Vehicles can include passive occupant restraints, such as airbags and air curtains. One type of passive occupant restraint is a side air curtain. Side air curtains may be mounted to a frame of the vehicle above a passenger compartment. For example, the vehicle may include a headliner above the passenger compartment, and the side air curtain may be mounted above the headliner. When an impact event is sensed, the side air curtain may be inflated. When inflated, the side air curtain extends downwardly from the headliner and may extend along doors and/or side pillars of the vehicle to cushion impact between an occupant and the doors and/or side pillars.
Several research organizations release test protocols and standards for vehicles. For example, the Insurance Institute for Highway Safety (IIHS) releases a standard for head injury criterion (HIC) to assess head injury risk in vehicle impact tests. HIC is a measurement of the likelihood of a head injury based on linear impact of an occupant's head. The HIC measurement is benefited by low translational head acceleration.
In 2012, IIHS also released a standard to measure brain injury criterion (BrIC). The BrIC measurement is benefited from low rotation of the occupant's head. Rotation of the occupant's head can occur, e.g., from side impact events. The National Highway Traffic Safety Administration (NHTSA) is updating its New Car Assessment Program (NCAP) to include BrIC criteria in addition to its already existing HIC criteria.
The NHTSA's NCAP criteria for BrIC may result in competing design factors for side air curtains than its criteria for HIC.